What makes the hind leg move? There are three basic phases of hind leg movement: the levation and depressing of the trochanter about the coxa, the rapid depressing of the trochanter about its coxa, and the extension and depression of the trochanter about its cox. The first two phases occur in less than a millisecond. The femur moves from the posterior position to the anterior position, which engages the lateral protrusion of the coxa. The entire levated position is maintained for two to three seconds, during which both hind legs extend and depress quickly.
Muscles
The muscle groups of the hind leg are referred to as hamstrings. The hamstrings are long, thin tendons that attach to the skeleton and constrain extension during the first half of stance. The distal end of the femur engages with a recess in the lateral head capsule to amplify this force. The muscles of the hind leg contribute to a variety of movement patterns and functions.
The anatomy of these muscles is complex, with numerous variations in their length and pennation angles. These differences may suggest functional specialization within the same muscle. Although a few studies of human muscle architecture have revealed the general anatomy of muscles, more detailed investigations of individual muscles would be necessary to understand the differences between these different types of hind limbs. Nevertheless, the authors suggest that further research is needed to determine their precise physiological functions.
Tendons
In humans, tendons in the hind leg are responsible for walking and running. They are long, longitudinal bundles of fibre that help maintain the shape of joints. Most of the tendons in the hind leg originate from the forelimb. They course down the carpal canal, cross the navicular bone, and insert on the coffin bone. They lie under the suspensory ligament and play a role in knee and forefoot flexion, as well as elbow extension and hock flexion.
While a horse’s hind leg tendon might look like an inactive, strained limb, it can sustain injury through strenuous exercise. In either case, strenuous exercise can tear the fibres and cause damage. Symptoms can range from mild tearing to total tendon rupture. The damage is most often localized and may appear as a discrete hole. As the tendons heal, they will begin to produce more collagen and rebuild.
Bones
The vertebral column of man is more than twice the size of its thoracic portion. In fact, the entire hind limb is transmitted to the spinal column, whose seven or eight carpal bones are arranged in two rows. Each carpal bone is a scapula, which articulates with the lower end of the second phalanx to form the croup. The femur is almost round, with a long axis of 80 degrees. The femur is classified based on structure and mobility, and its appearance resembles that of water.
The femur bone is the longest bone in the body, with two distinct ends and a middle shaft. The head of the femur articulates with the acetabulum, which is the joint that connects the leg to the rest of the body. The tibia, the smaller of the two bones, is joined to the femur by a ligament called the cnemial crest. Together, these bones form the knee joint.
Digital cushion
The equine digital cushion is made up of four different regions. The axial-distal, proximal, lateral, and medial regions of the hind leg were studied for their characteristics. The axial-distal region had more collagen and fewer elastic fibers than the other three regions. A mathematical mean was calculated for each region. Here are some examples of samples. Listed below are a few examples.
The digital cushion is the soft tissue that is located in the rear of the hoof. It acts as the main shock-absorbing structure in the hoof. When a horse’s toes are too long or its heel is too low, the digital cushion is likely compromised. Over time, the heel slowly compresses the digital cushion and prevents it from properly supporting the bone structure. If the cushion becomes crushed, it will not regenerate.
Joints
The joint in the hind leg is similar to the knee of a human. It consists of four bones: the femur, the tibia, the remnant fibula, and the femur-tibia joint. Each of these bones works together through three joints. The first, the femoropatellar joint, is designed to absorb shock and allow the horse to move smoothly. A joint capsule surrounds the joint, which is fairly deep inside the horse. Consequently, dislocation of the hip joint can cause severe damage.
The pelvic girdle includes the sacrum and the first three coccygeal vertebrae. The pelvic bones are made up of three flat bones: the ilium, pubis, and ischium. They are connected to the sacrum at the sacroiliac joint. The sacroiliac joint is supported by the ventral sacroiliac ligaments.